Field injection seems like a tidy way to get your classes what they need to do their jobs, but it's really a NullPointerException
waiting to happen unless all your class constructors are private
. That's because any class instances that are constructed by callers,
rather than instantiated by the Spring framework, won't have the ability to perform the field injection.
Instead @Inject
should be moved to the constructor and the fields required as constructor parameters.
This rule raises an issue when classes with non-private
constructors (including the default constructor) use field injection.
class MyComponent { // Anyone can call the default constructor @Inject MyCollaborator collaborator; // Noncompliant public void myBusinessMethod() { collaborator.doSomething(); // this will fail in classes new-ed by a caller } }
class MyComponent { private final MyCollaborator collaborator; @Inject public MyComponent(MyCollaborator collaborator) { Assert.notNull(collaborator, "MyCollaborator must not be null!"); this.collaborator = collaborator; } public void myBusinessMethod() { collaborator.doSomething(); } }